The use of plasma, which is generated by discharge, has been studied in connection with various applications including surface treatment of semiconductors, electronics devices and other electronic materials, bio-materials, new functional polymers and other materials, formation of thin films for developing new materials, decomposition of waste gas, and reaction of vapor-phase synthesis. As a result, plasma technology has been established practical basic applications in several areas.
Plasma techniques are known which utilize glow discharge plasma generated under a so-called high vacuum condition, including plasma CVD, ion plating, plasma etching, and plasma surface treatment.
These low pressure glow discharge plasma techniques are recognized as effective in producing surfaces and thin films of a relatively good quality. However, because it is necessary to maintain a low pressure condition, these techniques suffer drawbacks in that a vacuum system must be provided and maintained, in that it is difficult to sustain discharge, and in that a huge amount of cost is necessary to keep the system air-tight.
According to conventional knowledge, generation of glow discharge plasma generally requires a low pressure condition of several Torr or below. This is because the discharge concentrates on one point a pressure of about 100 Torr, and with rising pressure the discharge shifts to sparks and arc discharge at about atmospheric pressure, making it impossible to uniformly process an object.
Now therefore the inventor of the present invention has established a glow discharge plasma technique which can be used under atmospheric pressure to replace conventional low pressure glow discharge plasma techniques, and has actively studied its applications as well. As a result, the inventor has found that the atmospheric pressure glow discharge plasma of the invention is capable of performing highly efficient and high quality surface treatment, thin film formation, etc., without using a conventional and troublesome vacuum system, and has been studying commercialization of the technique in various fields. Since then, a new development has been made for also applying the invention to so-called waste gas processing and vapor-phase synthesis reaction.
However, to further develop this atmospheric pressure glow discharge plasma technique, a plasma reaction method that is capable of generating and utilizing plasma more accurately and capable of controlling the plasma in more diverse shapes must be developed. To generate and control plasma in this way, the state of plasma must first be monitored. Such monitoring is also indispensable in the conventional low pressure method, yet in the case of the atmospheric pressure glow discharge plasma, conventionally known unvoiced discharge and arc discharge must be accurately avoided since the atmospheric pressure condition is used. For this reason, the establishment of a monitoring method for atmospheric pressure glow discharge plasma has been an important task.